| As a special form of polymer, the perdeuterated polymer foams not only have the microporours structure and good capabilities as same as nondeuterated polymer foams, but have some particular characters, such as isotope effect, nonradioactivity, and high deuterated ratio. For those reasons, the perdeuterated polymer foams will be used in many fields, especially in inertial confinement fusion (ICF) and low wastage plastic. However, it is very important to find an easy and cheap procedure for preparing the polymer foams.In this paper, a route for preparation of the perdueterated low-density polystyrene foam, which contains the thermally-induced phase separation of polystyrene solution and freeze-drying of the solution, was brought forward to meet needs of ICF study in China. For the perdeuterated low-density foams, the structure morphology and capability were analyzed. In order to confirm the solvent of perdueterated polystyrene, the computer simulation method was used in qualitative analysis in the phase separation process for the different polystyrene-solvent systems. Meanwhile, some analytical methods, such as scanning electron photomicrograph (SEM), transmitting electron photomicrograph (TEM), pressing mercury method, specific surface area (BET) or others, were used for structure analysis of the prepared foams. Based on the results, the solvent system of dioxane and cyclohexane (44/56,V/V) is recommended. Also, other conditions for the preparation of the perdueterated low-density polystyrene foam were discussed. The results recommended that the cooling rate be higher than 100℃/min in order to attain the uniform net structure, the single direct cooling be propitious to reduce the effects brought by the different temperature between the center and periphery of solution, and the foam structure don't be affected by the molecular weight and disperse degree of perdueterated polystyrene. However, in order to attain the ultra-low density foam, the molecular weight of perdueterated polystyrene should be more than 300000. Furthermore, no obvious change of the deuterated ratio was noted in the process of the foam preparation, even if the nondeuterated solvents were used.Usually, with the perdueterated polystyrene of molecular weight of about 250000 and disperse degree of about 3 as the materiales, the opened-cell foams with density of 0.02 g/cm3~0.1g/cm3, the average cell size of 0.2~1μm, and the deuterated ratio of more than 98% could be fabricated.The thermally stable capability and mechanical property of the deuterated foam above were analyzed by the differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), stress-strain behavior analysis, and other methods. The results showed that the glass temperature or the decomposed temperature for the prepared foams is 100℃-120℃,or about 400℃, respectively. However, there was the irreversible change in the foams at between 50℃ and 100℃.Also, the Young's modulus was enhanced along with the increase of the foams density at room temperature (22℃). For example, there was change of 3-35% at the density of 20 mg/cm3 - 160 mg/cm3, and the Young's modulus of 2MPa -10MPa.In summary, this study established a fabrication method for perdeuterated low-density polystyrene foam. The resulted foams would meet the actual needs after the analyses of foams' structure and capability. All those study not only provided the new way for the fabrication of ICF targets in China, but laid a foundation for the perdueterated polymer foams used for other fields.
|
PDF Full Text Request